The Mojave Desert is the smallest of the four North American deserts. While the Mojave lies between the Great Basin Shrub Steppe and the Sonoran Desert, its fauna is more closely allied with the lower Colorado division of the Sonoran Desert. Dominant plants of the Mojave include Creosote Bush (Larrea tridentata), Many-fruit Saltbush (Atriplex polycarpa), Brittlebush (Encelia farinosa), Desert Holly (Atriplex hymenelytra), White Burrobush (Hymenoclea salsola), and Joshua Tree (Yucca brevifolia), the most notable endemic species in the region.

Joshua Tree National Park, California, USA. Source: John Morrison

The Mojave is bounded to the north by the Great Basin shrub steppe, to the west by the Sierra Nevada and California montane scrub, and to the east by the Colorado Plateau. To the south, the Mojave blends into the Sonoran Desert, with a combination of species typical of the two deserts plus species most often found in the scrublands or conifer woodland of the Great Basin. Mojave species generally favor the colder plains, while Sonoran species are found on hillsides.

The Mojave’s warm temperate climate defines it as a distinct ecoregion. Species that serve to separate the Mojave from the Sonoran desert include such widespread Sonoran species as Ironwood (Olneya tesota), Blue Palo Verde (Cercidium floridum), and California Water Willow (Justicia californica). Mojave indicator species include Spiny Menodora (Menodora spinescens), Desert Senna (Cassia armata), Mojave Indigobush (Psorothamnus arborescens), and Shockley's Goldenhead (Acamptopappus shockleyi).

The Mojave supports numerous species of cacti, including several endemics, such as Silver Cholla (Opuntia echinocarpa), Mojave Prickly Pear (O. erinacea), Beavertail Cactus (O. basilaris), and Cotton-top Cactus (Echinocactus polycephalus). The region is also rich in ephemeral plants, with around 80 to 90 endemic taxa.

The Mojave Desert contains a range of elevations not found in other North American deserts. Elevation ranges from below sea level in Death Valley (-146 meters to over 1600 meters in some montane areas). Most of the region lies between 610 and 1220 meters, giving rise to the term high desert. The Mojave receives little precipitation (between 65 and 190 millimeters per annum) and dry lakes are a common feature of the landscape.

Biological distinctiveness

A majority of the fauna found in the Mojave Desert also extends into the Sonoran or Great Basin deserts as well. There is a modest level of vertebrate species richness in the Mojave Desert, with a total of 380 vertebrate taxa having been recorded here. There are numerous special status organisms that are found in the Chihuahuan Desert, denoted as Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).

Arthropods

While the Mojave Desert is not so biologically distinct as the other desert ecoregions, distinctive endemic communities occur throughout. For example, the Kelso Dunes in the Mojave National Preserve harbor seven species of endemic insects, including the Kelso Dunes Jerusalem Cricket (Ammopelmatus kelsoensis) and the Kelso Dunes Shieldback Katydid (Eremopedes kelsoensis). The Mojave Fringe-toed Lizard (Uma Scoparia), while not endemic to the dunes, is rare elsewhere.

Flowering plants also attract butterflies such as the Mojave Sooty-wing (Pholisora libya), and the widely distributed Painted Lady (Vanessa cardui).

Lowland Leopard Frog. Source: William Flaxington/ EoL
Amphibians

There are a total of eight amphibian species present in the Mojave Desert all of which are anuranAn amphibian that has limbs but no tail (includes all frogs and toads)species: the endemic Relict Leopard Frog (Lithobates onca); the endemic Amargosa Toad (Anaxyrus nelsoni); Lowland Leopard Frog (Lithobates yavapaiensis); Red-spotted Toad (Anaxyrus punctatus); Southwestern Toad (Anaxyrus microscaphus); Great Basin Spadefoot (Spea intermontana); Great Plains Toad (Anaxyrus cognatus); and the Pacific Treefrog (Pseudacris regilla).

Reptiles

The native range of California’s threatened Desert Tortoise (Gopherus agassizii) includes the Mojave and Colorado Deserts. The Desert Tortoise has adapted for arid habitats by storing up to a liter of water in its urinary bladder. This tortoise consumes ephemeral plants in the spring and accumulates sufficient water reserves to last through the remainder of the year.

Flora

The Mojave Desert is rich in ephemeral plants, most of which are classified as endemic. Of the approximately 250 Mojave plant taxa with this ephemeral characteristic, approximately eighty to ninety are endemic. During favorable years, the region supports more endemic plants per square meter than any location in the United States. Most of these species are winter annuals. Western Poison Oak (Toxicodendron diversilobum) is a widespread vascular plant occurring in the Mojave Desert.

Conservation status

Skull Rock and desert scrub, Joshua Tree NM. @ C.Michael Hogan

Habitat loss and degradation

Roughly half of the Mojave Desert remains as intact habitat, and the remaining half has not been heavily altered by human activity. The main reasons for habitat loss in the region include urbanization and suburbanization from Los Angeles and Las Vegas, the increasing demand for landfill space (Los Angeles and San Diego have proposed a large landfill in the region), agricultural development along the Colorado River, grazing, offroad vehicles, and military activities. Areas under particular pressure include Ward Valley (near Mojave National Park) and Riverside Country, west of Joshua Tree National Monument. A falling water table also threatens Death Valley National Park.

Remaining blocks of intact habitat

The most important remaining intactThe condition of an ecological habitat being an undisturbed or natural environment habitat blocks include:

Death Valley National Monument - eastern California

Desert National Wildlife Range - southern Nevada

Joshua Tree National Monument - southeastern California

Lake Mead - southeastern Nevada and northwestern Arizona

Nevada Test Site - southern Nevada

Degree of fragmentation

Habitats in the Mojave desert are generally contiguous, with a high degree of connectivity. Roads, however, have fragmented habitat for certain species, such as desert tortoise and some species of snakes. Big horn sheep migration routes also are not adequately protected between reserves.

Degree of protection

By historical accident and the California Desert Protection Act, the Mojave desert is one of the best protected ecoregions in the United States. The full range of habitats are included in reserves, although riparian areas need more protection. In addition to the habitat blocks listed above, important protected areas include:

Kirgsten Range

Mojave National Park - southeastern California

Sheephole Wildlife Area - southeastern California

Greenwater Range

Lands covered under the California Desert Protection Act

Types and severity of threats

Conversion threats to the Mojave are concentrated in the southwest and east central portions of the ecoregion. Lower elevation valleys are largely in private hands and lack protection. The greatest present threat are proposals for large scale solar power arrays; such arrays not only reduce the biological powering of sunlight for desert flora and fauna, but destroy significant habitat areas by disturbing cryptobiotic soil crusts. Off-road vehicles and development threaten these valleys, and development also is harming creosotebush areas and the cryptobiotic crusts. Alien species such as tamarisk are invading springs, and grazing is damaging mid-elevation pastures. Wildlife trade threatens chuckwallas, gila monsters, and desert tortoises.

Suite of priority activities to enhance biodiversity conservation

The most important conservation activity in the Mojave desert is to protect riparian areas and low elevation valleys.

Conservation partners

California Desert Protection League

California Native Plant Society

The Wilderness Society

References

Vincent G. Mazzucchelli. 1967. The Southern Limits of the Mohave Desert, California. The California Geographer, 1967, VIII: 127–133. This study provides original maps of the Mohave and adjacent deserts in the southwestern states.

Disclaimer: This article contains some information that was originally published by, the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. Use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for new information added by EoE personnel, or for any editing of the original content.